Wilms tumor is the most common pediatric kidney cancer and is closely connected to kidney development. Mutations in two genes, WT1 and beta-catenin, and epigenetic changes in the insulin-like growth factor 2 (IGF2) locus have been described but the genetic basis of the majority of cases remains unknown. Given that current treatment protocols for Wilms tumor achieve high success rates (85%), there is a pressing need for prognostic markers that can guide clinical management but these have been difficult to define. We have recently identified a novel tumor suppressor located on the X chromosome, WTX, which is inactivated in 30% of Wilms tumor cases. We now propose to build on our initial findings to establish clinical correlates of WTX inactivation and to test the potential application of WTX mutations as markers of prognosis. We will also define additional markers by identifying molecular pathways that are affected by WTX inactivation Together, these studies will achieve immediate translational goals by defining novel biomarkers in Wilms tumor and will further our understanding of this disease to allow the future development of biologically based therapies. Specific aims: 1) To define clinical correlations of WTX inactivation in Wilms tumor. We will analyze 200 Wilms tumors for WTX mutations and correlate our findings with disease outcomes and other clinical parameters such as age at presentation, stage at diagnosis, bilaterality and associated developmental malformations. We will also develop a WTX polyclonal antibody and a Wilms tumor tissue microarray to test WTX protein levels. 2) Modeling WTX function to identify pathways of potential clinical significance. We will use immunoprecipitation of tagged WTX followed by mass spectrometry to define interactions between WTX and other cellular components. The functional consequences of these interactions will be validated in vitro using kidney derived cell lines and in vivo using a WTX conditional knockout mouse. 3) Clinical validation of novel Wilms tumor markers. Genes involved in WTX related pathways will be tested for potential clinical applications as biomarkers by correlating expression levels with clinical parameters. We will also test selected genes for mutations in primary Wilms tumors. We anticipated that, by defining prognostic markers and furthering our knowledge of WTX related pathways in Wilms tumor, this project will have public health applications in the treatment of pediatric kidney cancer.